This invention relates to the matched metal die molding of composite articles, and more particularly to compression molding a special purpose (e.g., cosmetic, hard, abrasion-resistant, etc.) skin of one polymer onto a surface of another freshly-molded, compatible polymer. Such a technique has been found desirable, for example, in providing cosmetic (i.e., substantially blemish-free or colored) coatings to freshly-molded articles whose as-molded surfaces are aesthetically undesirable for reasons such as porosity resulting from uneven plastic flow, sink marks due to shrinkage occurring at joints and/or discolorations or blemishes due to impurities in the molding material and/or high filler loadings.
The process of improving the surface of compression molded articles by compression molding a cosmetic skin thereover to cover or fill any imperfections therein is well known in the art. Fischer U.S. Pat. No. 3,184,527, for example, discloses introducing a blob of skin-forming material into the mold after the base article has either fully or partially set-up (i.e., cured or solidified) followed by compression molding the blob over and to the surface being coated. Such processes, however, are unnecessarily time consuming, require unnecessary mechanical means to immobilize the first-molded article or substrate in place in the mold during complete opening thereof and are susceptible to the incursion of contaminants (e.g., flash, dirt, etc.) into the mold during opening and the placement of the blob in the mold.
It is an object of the present invention to provide an automatic, in-mold coating process for providing a freshly-molded polymeric substrate with a skin of desired properties in a simple, quick and accurate manner without dislodging the substrate in the mold or rendering it accessible to the contamination between molding and coating.